That's not entirely my reason for not caring as much for the Namor / Sue relationship, but yes, that does seem to be what a lot of people know him for. Of course, it's usually how he is introduced in cartoons, also. The double edged sword of popular exposure.
Sadly, it is always going to be brought up, because some writers want to use him to liven up Reed and Sue's relationship. Sue also isn't above using Namor to do so. Also, it is a way to bring Namor into whatever is going on with the FF. I don't know if they have a _great_ friendship, but Namor will always having feelings for her, just as he has feeling for his two deceased wives, and Betty Dean, and Tamara, and Diane Arliss, and all the ladies in his life. And of course, to be fair, Namor WOULD start a more than platonic relationship with Sue, IF Sue wanted to.
I agree with the bolded, but I don't think that is what bothers people about Namor and Sue's relationship. No one wants to be 'left' in a relationship, and few blame themselves when it happens. So, they blame the guy their SO left with, instead looking at what went wrong with the relationship. There may be a bit of projecting going on.
And Reed is almost always cast as the absent minded husband, who sometimes forgets his family while working. Oddly, Bendis, or maybe it was Reed, on their Illuminati mini-series.